Optical resonances in nanoparticles may lead to a new class of extremely sensitive sensors for studying interactions between nanomaterials and gases and liquids during catalytic reactions in real-time under realistic conditions, say researchers in the chemical physics group at Chalmers University of Technology, Gothenburg, Sweden. Use of so-called localized surface plasmon resonance (LSPR) should enable development of robust and inexpensive sensing chips, they add.
The Swedish team relies on what it calls an entirely new approach to using LSPR with catalysts. Besides sensing changes in catalyst nanoparticles themselves, their method looks at the catalyst support. This indirect approach is much more versatile, the researchers claim.
The sensors consist of arrays of nanofabricated gold disks with a thin (about 10 nm.) coating on to which catalysts nanoparticles are deposited. In principle, they can work with any nanocatalyst because the underlying phenomenon — a change in the composition of the chemsorption or thin surface layer altering the polarizability/dielectric properties of that layer sensed by the LSPR (Figure 1) — occurs with all catalytic materials, the researchers note. Changes in surface coverage of less than 0.1 atomic monolayer were easily detected under high pressure, sensitivity unrivalled by commercial instruments under those conditions, says Elin Larsson, who now works at the Competence Center for Catalysis at Chalmers. Sensitivities, of course, will vary with particular system. There're no limitations in what can serve as support material; alumina, titania, zirconia, iron oxides and various carbides will work as well as the SiO2 used in their tests, the researchers add. Sensing structures used so far haven't been optimized as to shape, size, material of the LSPR sensing particles or separating layer.
"The technique itself is very inexpensive since it uses light transmitted through or reflected from a tailor-made sensing chip. The optical equipment is fairly cheap and since the sensing chip can be made very small and only small amounts of material are needed it too can be made at low cost. The robustness comes from the design of the sensing chip and also from the fact that the sensitive optical equipment does not need to be located inside the test environment, i.e., remote sensing is applied," says Larsson.
Besides further developing the indirect sensing platform for catalysis duties, researchers at Chalmers are applying it in hydrogen storage applications, she notes.
The researchers aim to commercialize high-sensitivity research instruments based on technology through the "CleanSense" project, a collaborative venture with entrepreneurs that was founded in 2008 to bring such developments to market. "We will have the first instruments out at customers' laboratories in the end of 2010," Larsson says.